On 7 September 2015 at 15:49, Timothy Baldridge <tbaldri...@gmail.com>
wrote:
>
> Types are good even in dynamic languages, we should use the more. As
> mentioned by Thomas, records are the idiomatic way to store typed
> information in Clojure.
>
I don't think that's true. Or rather, I think it depends on what you mean
by "type".
In core.typed parlance, a "type" is a means of validating the shape of data
at compile time. We can use a vector to represent a variant, and still have
it typed:
(defalias FooResult
(U '[(Value :ok) Int]
'[(Value :err) Str]))
Dynamic typing libraries like Schema or Annotate have a similar notion of
types, but perform their checks at runtime. In both cases, the type is
independent of the data; we can determine whether a data structure matches
a specific type, but the type isn't tied to the data.
In contrast, we have a notion of what core.typed and edn calls a "tag",
which is attached directly to the data structure. A record is essentially a
tagged map, and if we didn't have to worry about performance, tags would
probably just be implemented as metadata.
If we're talking about records, then we're talking about tags more than
types, and the question becomes: what data should we tag?
If we want runtime polymorphism, then it makes sense to use a tag so we
have something to dispatch off. But is there any other practical reason
we'd want to use a tagged structure in Clojure?
I'm not convinced there is. Records are useful for polymorphism, and
perhaps performance if that level of optimisation is necessary, but I don't
see any other benefit.
> The above video is a exploratory explanation of a different way of
> thinking of data, but I have never seen code like that in production, and
> it's so different from idiomatic Clojure, that I would be hesitant to adopt
> it wholesale.
>
A lot of people use Instaparse and Hiccup in production, which I believe
the video explicitly mentions as being examples of variants.
- James
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